MG Midget and Sprite Technical valve seals BBS discussion at MG-Cars.net

MG Midget and Sprite Technical - valve seals

WRT to valve seals and external rocker feeds on the Triumph 4-pot... Standard Triumph (later BL) never fitted them because: 1. They saw no need (albeit earlier Standard Triumph designs DID use external rocker feeds, eg on the Triumph Roadster made famous by the Bergerac TV series). 2. With the later (1147cc engines onwards), the use of double valve springs precluded fitment of seals. Moss state that MGB seals can be used, but as Peter says, this would result in about the square root of F all effect (other than on your wallet). As you have found, the use of the Moss rocker feed kit has resulted in excessive top end oiling which is the root of your problems. While it IS a fact that these motors DO suffer rocker and shaft wear owing to poor lubrication, which can be abrogated by a better feed (and indeed an external feed IS required for roller rockers), as I have stated INNUMERABLE times on this forum EVERY, repeat EVERY, commercially available rocker feed kit, whether from Moss, Rimmer Brothers, or the like, is FUNDAMENTALLY flawed. To understand why this is so, one has to understand the history behind Moss becoming Triumph agents (when originally they dealt purely with the MG and A/H marques: 25+ years ago Moss were based in Richmond and were co-located in the building with a company known as 'TriumphTune'. TriumphTune (as the name purports) reckoned themselves to be the masters of anything performance related to Triumphs and were run by a gentleman called Terry Hurrel. Now Terry, while he reckoned himself knowledgeable, was in fact a bit of a bandit who would sell unsuspecting punters any old piece of tat which was claimed to 'improve' their vehicle. Unfortunately most of this tat DID NOT work, and in many cases de-tuned the vehicle! Indeed the 'TriumphTune Performance Manual' of the time was a source of great mirth to those of us actually racing Triumphs! Terry also traded upon the fact that he was the son of Sydney Arthur Hurrel who had, in the 1960's, run SAH Engineering in Leighton Buzzard. SAH had, in fact, been a very good outfit who had worked closely with ex-members of the Triumph Competitions Department to bring the Le Mans and Rally inspired tuning parts to the general public. Unfortunately Terry did not have Sydney's engineering skills or knowledge. Even more unfortunately Terry suffered a stroke some years back so the TriuphTune brand was taken over by Moss lock stock and barrel. The upshot of this is that the TriumphTune designed rocker feed kit, which is as I have stated fundamentally flawed, was farmed out in terms of production to Think Automotive, and is now sold by all the 'major players'. So why is this rocker feed kit flawed? There are 3 reasons: Firstly it uses a -3 hose with a banjo fitting to go into the oil gallery plug at the back of the head and a 1/8 NPTF fitting to screw into the main oil gallery beneath the distributor (with an adapter for the oil pressure gauge hose/oil pressure sender). Thus it INEVITABLY robs oil from the gallery supplying the centre main bearing (and, thus, big ends nos 2 and 3). This is a VERY BAD idea ESPECIALLY on the 1500 motor because the centre main feed is ALREADY pretty marginal. So fitting the kit this way makes your motor MORE likely to go 'pop'! Secondly the kit has no restrictor in it which leads to excessive top end oiling, causing problems with inlet valve stem oiling at low rpm with the resultant high oil consumption, possibility of detonation caused by oil lowering the RON of the inlet charge, as well as increased chances of rocker box gasket leaks. Thirdly, merely bolting such a kit to your motor takes NO ACCOUNT of the fact that there is an INTERNAL oilway to the rockers that is still active. This will cause cavitation in the oil galleries and ALL SORTS of flow problems! Thus you can see that the kit is about as much use as a chocolate fireguard in its supplied form. Indeed I don't feel that an external rocker feed is at all necessary on a stock motor, although it is beneficial on tuned or race motors. If you really want to fit an external feed then the correct way to do it is as follows: Firstly the internal oil feed to the rockers must be blocked off in both the head and the block. I tap both and fit 8mm grub-screws loctited in place. Secondly the oil feed to the centre main needs to be opened out to improve flow. To do this the distributor pedestal bush has to be removed; the oilway can then be reamed out to 5/16" (7.9 mm). Take care re-fitting the bush and ensure you set the distributor endfloat correctly. Thirdly the external oilfeed should not come off the main gallery opposite the centre main, but from the aft-most tapping opposite no 3 main at the rear of the block. Additionally a restrictor needs to be fitted. Fortunately taking the oilfeed from the rear tapping means you are tapping into a 5/16" drilling, so to fit the -3 hose you require a -2 to -3 male-male adapter which itself restricts the oil flow, thus killing two birds with one stone. Additionally it is beneficial to machine a groove into the flat area of the cylinder head top face (on the manifold side). This helps reduce oil 'puddling' on the head and assists flow back to the sump via the tappet bores. Doing the above will turn what is a very bad piece of engineering into something that does what it says on the tin. There may still be SOME concerns about over oiling the top end at low RPM although this isn't such a worry on a race motor. Currently I am looking at using a Mercedes stem seal that will fit over the top of the inlet valve guide, however this will mean better location of the inner valve spring is required than that provided by the stock valve base, ie a new design of valve base. Having said that, new valve spring bases are required anyway if you use any of the aftermarket uprated valve springs (Iskenderian, Kent) because the inner springs supplied by such are longer than stock, so using the Triumph spring base throws the seat pressures out of whack (meaning increased likelihood of cam wear/lobe failure), whilst not using a spring base (as advised by Kent) leads to poor location and the spring coil 'eating into' the head face. A couple of photo's; This is the WRONG way to fit an external rocker feed, taking the feed from the tapping below the distributor pedestal:

Deborah Evans

This is the RIGHT way to do it, taking the feed from the aftmost main gallery tapping:

Deborah Evans

Deb would you consider writing an article for MASCOT the magazine of the midget And Sprite Club please? :-) I'm sure Gary would be very grateful So would I and lots more of us I enjoy reading your exposés very much I'm amazed and chastened that I must have met you (along with several of us on here) at Peter May's first Christmas Pies Party, withoout realising it... picture some cars from the first PM Xmas Meet

bill sdgpm

Apologies for being off topic. Here is my mgtf 160 that was at that Peter May Xmas event. The car has been tuned to 185 bhp NASP (as far as you can go while retaining the VVC mechanisms) but punches out around 250 bhp (and 225 ft.lbs torque) on Nitrous. Here we are at Brands coming off the apex of Paddock Hill at around 120 mph (before snatching 5th) in the wet:

Deborah Evans

This thread was discussed between 14/06/2010 and 17/06/2010

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